Obtain boolean value of expression in PLPGSQL

[Max Speransky]

Hello

My task is to validate expression and get value of it in boolean variable.
I try to do following:
CREATE OR REPLACE FUNCTION get_value(integer) RETURNS boolean AS'
DECLARE
Ret boolean;
Op TEXT = ''='';
BEGIN

Ret := 3 || Op || $1;
RETURN Ret;
END;
' language 'plpgsql';

when I try to execute this function I get such result:

bill=# select get_value(3);
WARNING: Error occurred while executing PL/pgSQL function get_value
WARNING: line 6 at assignment
ERROR: Bad boolean external representation '3=3'
bill=#

So, how can I explain that resulting type must be boolean ? Also, I try to
play with SELECT INTO with same result.

--
.... All opinions expressed are mine and not those of my employer.

Yours, Max [Msg N 2419]
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[Richard Huxton]

On Tuesday 04 November 2003 10:06, Max Speransky wrote:

Hello

My task is to validate expression and get value of it in boolean variable.
I try to do following: Ret := 3 || Op || $1;
RETURN Ret; bill=# select get_value(3);
WARNING: Error occurred while executing PL/pgSQL function get_value
WARNING: line 6 at assignment
ERROR: Bad boolean external representation '3=3'

The problem is that your expression is being evaluated as a string. In the
absence of an eval() function, you probably should do something like:

my_stmt := ''SELECT '' || 3 || Op || $1;
EXECUTE my_stmt;
FOR EACH ...

So - build a simple query, execute it and read the result. Should do what you
want.

--
Richard Huxton
Archonet Ltd

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[Pavel Stehule]

Hello

You are on wrong way.

Try like

DECLARE
b RECORD;
s TEXT;
op TEXT;
BEGIN op := ''='';
s := ''SELECT 3 ''|| op || ''|| $1 || ''AS b'';
FOR b IN EXECUTE s LOOP
RETURN b.b;
END LOOP;
END;

Regards
Pavel
On Tue, 4 Nov 2003, Max Speransky wrote:

Hello

My task is to validate expression and get value of it in boolean variable.
I try to do following:
CREATE OR REPLACE FUNCTION get_value(integer) RETURNS boolean AS'
DECLARE
Ret boolean;
Op TEXT = ''='';
BEGIN

Ret := 3 || Op || $1;
RETURN Ret;
END;
' language 'plpgsql';

when I try to execute this function I get such result:

bill=# select get_value(3);
WARNING: Error occurred while executing PL/pgSQL function get_value
WARNING: line 6 at assignment
ERROR: Bad boolean external representation '3=3'
bill=#

So, how can I explain that resulting type must be boolean ? Also, I try to
play with SELECT INTO with same result.

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[Martin Hart]

Max Speransky said:

Hello

My task is to validate expression and get value of it in boolean variable. [snip] when I try to execute this function I get such result:

bill=# select get_value(3);
WARNING: Error occurred while executing PL/pgSQL function get_value
WARNING: line 6 at assignment
ERROR: Bad boolean external representation '3=3'

|| is the string concatenation operator - so your expression creates a
string "3=3" and then tries to return that as a boolean hence the error.

if you cannot just do "return 3 = $1;" perhaps you could try using EXECUTE?

cheers
Martin
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